The present invention relates to polishing methods and polishing devices, and in particular relates to planarization during manufacturing processes for semiconductor devices.
Recent advances in the miniaturization of semiconductors have led to an increase in the number of process steps in semiconductor manufacturing processes and have made the processes more complex. As a result, problems caused by unevenness (steps) present in the surface of semiconductor devices (such as variation in resist dimensions when patterning with photolithography, and wiring shorts at step portions), which have conventionally not been of particular concern, are becoming noticeable. Thus, in recent semiconductor manufacturing processes, a high degree of planarization of the semiconductor device surface is imperative.
Chemical mechanical polishing (hereinafter abbreviated as CMP) is a widely employed polishing method for planarizing the surface of semiconductor devices during semiconductor processing. A conventional polishing method using CMP is described with reference to FIG. 8.
As shown in FIG. 8, a polishing device 200 using conventional CMP is provided with a polishing plate 109, a polishing pad 110 that is adhered to the polishing plate 109, a carrier head 112 for holding the wafer to be polished, and a slurry supply chute 113.
The polishing plate 109 is rotated about a rotational shaft A1. A wafer 111 is held by the carried head 112. The carrier head 112 is provided with a rotational shaft A2 and rotates about this rotational shaft, and pushes the wafer 111 against the polishing pad 110 with a prescribed force as the rotational shaft A2 is moved back and forth.
In this state, slurry 114 that is supplied onto the polishing pad 110 from the slurry supply chute 113 disseminates over the polishing pad 110 and seeps between the polishing pad 110 and the wafer 111. Thus, the wafer 111 is polished. In other words, favorable polishing is accomplished through the dual action of mechanical polishing due to relative motion between the polishing pad 110 and the wafer 111 and the chemical action of the slurry 114.
However, in conventional CMP processes, as polishing of the wafer 111 proceeds, friction occurs at the polishing pad 110 and the amount that the wafer 111 protrudes from the carrier head 112 is changed. Consequently, after a certain period of time, the polishing pad 110 must be replaced and the amount that the wafer 111 protrudes from the carrier head 112 must be adjusted. At that time, technicians are relied on to manually attach the polishing pad 110 to the polishing plate 109 and to assemble the carrier head 112. Thus, even if the pressure at which the carrier head 112 pushes the wafer 111 against the polishing pad 110 and the speed at which the polishing plate 109 and the carrier head 112 are rotated are set to identical conditions and polishing is performed, the distribution of the thickness polished in a set period (hereinafter, referred to as the polishing rate) on the polishing surface of the wafer 111 is changed, and this is not easily corrected.
A method of correcting and controlling the polishing rate is disclosed in JP 2001-60572A. According to this method, during polishing, the thickness of the film that is being polished on the wafer is monitored and compared to a target film thickness distribution, and by adjusting the pressure inside the chamber holding the wafer provided on the carrier head, a polished surface of a desired flatness is obtained.
This method can be used to solve the foregoing conventional problems, however, it also has the following drawbacks.
First, with this method, if the film thickness distribution that is obtained differs from the target, then the pressure within the chamber is altered during polishing so as to draw the film thickness distribution closer to the target. At this time, the equilibrium of the force due to the relative motion acting between the polishing pad and the wafer is upset, and irregular polishing (such as a polishing rate locally above predicted values) occurs as a consequence. In the worst cases, there is a risk that the wafer may break or be detached from the carrier head, for example.
Also, during the CMP process, environmental factors such as changes in temperature during polishing may cause the polishing rate to change. Consequently, environmental parameters being changed by altering the pressure within the chamber during polishing, as in the above method, results in an increase in the number of unstable factors when polishing.
Moreover, according to this method, measurement during polishing of the film thickness of the film that is polished is achieved by measuring the intensity of the light that is reflected from numerous sampling zones on the wafer and converting this measured intensity into the film thickness. With this method of measurement, because the wafer is rotated during polishing, it is not possible to control at what parts of an actual wafer that is provided with patterns the light beam emanated from the light source is irradiated. For example, assuming a step for polishing an interlayer insulating film during a wiring step, the measured value of the film thickness of the interlayer insulating film will differ by an amount corresponding to the thickness of the wiring depending on whether the light beam is irradiated onto the interlayer insulating film deposited on the wiring or is irradiated onto the interlayer insulating film that is deposited on a region where the wiring is not formed. That is, the measured value will always include an error corresponding to the amount of wiring thickness. Thus, the above method is not suitable when precise film thickness control is required.